AOD-9604: structure, nomenclature and handling

The parent is human growth hormone, a protein of 191 residues and roughly 22 kilodaltons — a folded protein, not a peptide, and two orders of magnitude larger than most of this catalogue. AOD-9604 corresponds to its carboxyl-terminal region, residues 177 through 191, with one addition: a tyrosine placed at the amino terminus of the fragment. That gives a sixteen-residue peptide with a molecular weight of approximately 1,815 daltons.

The fragment inherits two cysteines from the parent — the residues at positions 182 and 189 in the protein's numbering — and in the correctly made peptide they are joined by a disulfide bond. The bridge closes an eight-residue loop within the chain, so the molecule is conformationally constrained in the same spirit as a cyclic peptide, but by a sulphur–sulphur bond rather than a backbone or side-chain amide. Everything distinctive about this compound analytically follows from that bond: it can be present, absent, or formed in the wrong place, and those are three different molecules.

The fragment-versus-parent distinction is the same one that arises with other fragment products: a 1.8-kilodalton peptide and a 22-kilodalton protein share a name lineage but are unambiguously separated by mass, and the certificate's stated theoretical figure identifies which entity a batch is.

The material is catalogued as AOD-9604 and AOD9604, and in fragment notation as Tyr-hGH(177-191) — a name that states the construction explicitly: tyrosine plus the parent's 177-to-191 stretch. It carries CAS 386264-39-7. As with most synthetic peptides, it is typically isolated as an acetate salt, which affects the mass weighed out without altering identity.

The parent protein appears in the literature as human growth hormone, hGH and somatotropin. Those names belong to the 191-residue protein, and listings using them for the fragment are imprecise in a way the registry number and the theoretical mass resolve.

Mass spectrometry confirms the intact molecular mass, and for a disulfide-bridged peptide the measurement reads on the bridge itself. Forming the bond releases two hydrogens, so the bridged peptide is two daltons lighter than its fully reduced counterpart — a small but defined difference that adequate resolving power detects. An observed mass matching the reduced form indicates the bridge never formed.

High-performance liquid chromatography resolves the main peak from related substances and yields the purity figure. Beyond the deletion sequences familiar to any sixteen-residue synthesis, the compound-specific related substances are the disulfide variants: the reduced open-chain form, and dimers, where the bridge formed between two chains rather than within one. Interchain pairing is the characteristic failure mode of cysteine-containing peptides, and it is chromatographically visible — dimers elute apart from the monomer and carry exactly twice its mass, so the two methods corroborate one another on this point.

HEEZ Research supplies AOD-9604 in a single format: a 5 mg lyophilized vial. There is no second strength in the current catalogue, so the format decision that arises with two-size products does not apply here.

The material is supplied as a lyophilized powder. Freeze-drying removes water and leaves the peptide as a solid, markedly more stable than the same peptide in solution, and stable enough at ambient temperature to ship without refrigeration in transit.

Reconstitution converts the dried cake into a working solution, and it is a standard laboratory step rather than a product specification. Which solvent is used, and at what final concentration, is determined by the protocol in force at the receiving facility.

What HEEZ specifies is the contents of the vial: lyophilized AOD-9604 in a single 5 mg format, stated on the label and on the batch certificate of analysis. Where a protocol is expressed in molar rather than mass terms, the additional figure it needs is the molecular weight, which the certificate records for the batch supplied.

One consideration is specific to disulfide-bridged peptides. Reducing agents cleave the bridge, so glassware or media carrying residues of dithiothreitol or similar reagents from earlier procedures will quietly convert the constrained peptide into its open-chain form. Dedicated or thoroughly rinsed labware avoids an interference that is invisible until the material is analysed again.

Sealed lyophilized AOD-9604 is ambient-stable for the duration of transit, so no cold chain or insulated packaging is required for shipping. On receipt the vial goes to refrigeration and is kept out of direct light.

Reconstituted material is held refrigerated and used within the window the receiving facility's protocols specify, and repeated freeze-thaw cycling is avoided. Solutions are treated as short-lived relative to the lyophilized form.

The bridge adds one storage-specific behaviour: disulfides exchange under alkaline conditions, where free thiols catalyse reshuffling between and within chains. Solutions of this compound are therefore not held at high pH, and the robust-looking loop should not be mistaken for general chemical inertness — the standard peptide handling above applies in full.

The certificate records what an independent facility measured for one specific batch. Its value lies in being batch-specific, so the first check is that the lot number on the document matches the vial in hand.

The identity section compares observed molecular mass against a stated theoretical mass, which should correspond to the bridged sixteen-residue fragment near 1,815 daltons — the oxidized, disulfide-closed form, not the reduced chain two daltons heavier, and not the 22-kilodalton parent.

The purity figure is the HPLC main-peak area as a percentage of total peak area, and the attached chromatogram shows how that figure was arrived at. On this compound the peaks worth noting are any at twice the target mass, indicating dimer, and any close-eluting peak consistent with the open-chain form.

Peptide content, or net peptide content, is sometimes reported separately. It accounts for counter-ions and residual water, and it is the figure determining how much actual peptide a nominal 5 mg represents.